Ion-channels are important therapeutic targets. Neuronal communication, heart function, and memory all critically rely upon the function of ligand-gated and voltage-gated ion-channels. In addition, a broad range of chronic and acute pathophysiological states in many organs such as the heart, gastrointestinal tract, and brain involve ion channels. Indeed, many existing drugs bind receptors directly or indirectly connected to ion-channels. For example, anti-psychotic drugs interact with receptors involved in dopaminergic, serotonergic, cholinergic, noradrenergic and glutamatergic neurotransmission.
Because of the importance of ion-channels as drug targets, there is a need for methods which enable high throughput screening (HTS) of compounds acting on ligand-gated and voltage-gated channels. However, existing HTS drug discovery systems targeting ion channels generally miss significant drug activity because they employ indirect methods, such as raw binding assays or fluorescence-based readouts. Although as many as ten thousand drug leads can be identified from a screen of a million compounds, identification of false positives and false negatives can still result in a potential highly therapeutic blockbuster drug being ignored, and in unnecessary and costly investments in false drug leads.
Patch clamp methods are superior to any other technology for measuring ion channel activity in cells, and can measure currents across cell membranes in ranges as low as picoAmps (see, e.g., Neher and Sakmann, Nature 260: 799-802; Hamill, et al., 1981, Pflugers Arch 391: 85-100; Sakmann and Neher, 1983, In Single-Channel Recording pp. 37-52, Eds. B. Sakmann and E. Neher. New York and London, Plenum Press).
Attempts have been made to use patch-clamp recordings in HTS platforms. For example, Sörensen et al., in WO 96/13721, describe a system that couples an HPLC autosampler to a micro-flow chamber in which a patch-clamped cell is placed. While the system enables multiple compounds to be assayed at a time, the system creates large dead volumes and solution exchange is generally slow compared to activation times of ion channel receptors.
Another strategy to develop patch-clamp-based HTS systems involves microfabrication of a plurality of patch-clamp-electrodes on solid supports using microfabrication techniques. Klemic, et al., in WO 01/59447, describe one such planar patch clamp electrode array comprising a plurality of electrodes for performing patch clamp recordings on a plurality of patch-clamped cells. Samples of cells and solutions are provided to the array by pouring, immersing the electrodes, or pipetting into wells containing the cells and electrodes. However, using such planar surfaces it has been difficult to obtain stable recording configurations for prolonged periods of time with good electrical properties.
In addition to difficulties observed in attempts to increase the throughput of patch clamp assays, the noise associated with recording electrodes is significant in most systems currently used and will often be the dominant source to the total noise in most electrophysiological measurements.